This invention relates to the fabrication of thin films of magnetic material by sputter deposition.
To increase the areal recording densities in both longitudinal and perpendicular magnetic information data storage media, a reduction in the recording film thickness is desirable. However, as the film thickness is reduced for narrow transition parameters in both longitudinal and perpendicular recording films, the magnetic volume energy (KUxc3x97V) of magnetic grains in the films can be less than the thermal fluctuation energy (KBxc3x97T) of the magnetic recording media, which limits storage density due to superparamagnetic effects. The magnetic energy should be larger than thermal fluctuation energy to safely store information in the recorded magnetic bit pattern. This can be expressed as:
(KUxc3x97V) greater than (kBxc3x97T)xe2x80x83xe2x80x83(Equation 1)
where, KU is the magnetic anisotropy energy of a magnetic grain; V is the magnetic grain volume; kB is Boltzman""s constant; and T is the absolute temperature.
To enhance the magnetic energy in ultra thin storage films, the development of recording films with large magnetic anisotropy energy has received much attention. Among the recording films, an L1o phase ordered FCT (Face Centered Tetragonal) FePt film is a strong candidate for high anisotropy energy films beyond 107 ergs/cc.
FePt thin films can be fabricated though sputter deposition. An as-deposited FePt film forms a chemically disordered FCC (Face Centered Cubic) crystallographic structure with soft magnetic properties in its hysteresis loop, such as a coercivity of less than a few hundred Oe. It is well known that an external thermal energy supplement, such as by pre-heating a substrate, in-situ heating of a growing film, and/or post-annealing of the as-deposited film, can convert the disordered FCC film structure to a chemically ordered FCT film structure which shows a large magnetic coercivity and an anisotropy energy beyond 5.0 kOe and 107 ergs/cc, respectively. The changes in coercivity and/or anisotropy energy can be regarded as being proportional to the degree of FCT transformation in the FePt film.
Thin film fabrication processes using external thermal energy supplements, such as the pre-heating a substrate, in-situ heating of a growing film, and/or post-annealing of an as-deposited film, have been used for Cr segregation in CoCr based alloy films and phase transformation in FePt based alloy films. However, such external energy processes limit the deposition environments in terms of high temperature facilities and materials, and add fabrication cost.
Because the currently used external heating methods require treatment using temperatures beyond 600xc2x0 C. and long heat treatment times of more than 1 hour to achieve high coercivity and/or anisotropy energy, the fabrication of such films usually requires expensive film production equipment and high system maintenance costs, which are not practical for the large scale production of the film. To reduce the required temperature and time parameters, an alternative method to fully or partially compensate for the external energy supplements should be developed.
Thus there is a need for a thin film fabrication process, which can fully or partially compensate for the external energy supplement in the manufacture of information data storage media, including magnetic and optic recording films.
This invention provides a method of manufacturing a thin film of magnetic material, comprising sputtering magnetic material from a target to a substrate to form a thin film of the magnetic material on the substrate, wherein the ratio of sputtering power in Watt to sputtering pressure in mTorr is greater than one. The target can include at least two of: Fe, Co, Ni, Cr, Pt and Pd. The sputtering pressure can be greater than 100 mTorr. The sputtering power can be greater than 300 Watts. The thin film can comprise a face centered tetragonal structure, including at least two of: Fe, Co, Ni, Cr, Pt and Pd. The substrate can comprise one of: glass, MgO, or silicon. The thin film can have a magnetic coercivity greater than 10 kOe. The method can further comprise annealing the thin film. The thickness of the thin film can be in the range of 5 nm to 200 nm.
Thin films of magnetic material made according to the method and magnetic storage media including a thin film of magnetic material made according to the method are also included.
In another aspect, the invention encompasses a thin film of magnetic material comprising a plurality of face centered tetragonal particles produced by thermalizing face centered cubic particles in a plasma during a plasma deposition process. The particles can comprise an alloy selected from the group of: FePd, FeNiPt, FeNiPd, CoPt, CoPd, CoNiPt, and CoNiPd. The thickness of the film can be in the range of 5 nm to 200 nm.